1. Field of the Invention
The present invention relates, in general, to a wire cable for window regulators of automobiles and, more particularly, to a wire cable for such window regulators, using a highly flexible, high-strength synthetic resin filament as the core element wire of its core strand; the core strand being also compressed to deform the cross-section of its element wires and bring the element wires into surface contact with each other in place of point contact, thus improving the flexibility of the wire cable, in addition to the fatigue resistance of the wire cable necessarily enduring a repeated bending action during an operation.
2. Description of the Prior Art
As well known to those skilled in the art, wire cables, used for controlling the operation of a variety of machines or implements, necessarily endure a repeated bending action since they continuously pass over power transmitting rotors, such as sheaves, drums or pulleys, while being tensioned during the operation of said machines or implements. Therefore, the wire cables for such machines or implements must have somewhat high resistance to wear and tear, breakage and frictional abrasion.
In the prior art, the strand structures of the wire cables for such machines or implements have been typically classified into three types: a parallel twisted structure formed by twisting a plurality of element wires together into a wire cable, a single-layer twisted structure formed by twisting a plurality of external element wires around a core element wire, and a multi-layer twisted structure formed by twisting a plurality of internal and/or external strands around a core strand. A single-layer annular strand cable is included in the multi-layer twisted cables, and has been preferably and widely used for controlling the operation of small-sized machines, such as window regulators of automobiles.
The single-layer annular strand cable is produced by twisting a plurality of external strands around one core strand such that the external strands form an annular single layer around the core strand. In the single-layer annular strand cable, each of the external and core strands consists of a plurality of element wires having circular cross-sections with similar diameters. The core element wire of each strand of such a single-layer annular strand cable may comprise one or three filaments. Of the two types of strands having one or three filaments as the core element wire, the strand having one filament as the core element wire has been more preferably used. In addition, one hemp filament in place of the three filaments has been preferably used as the core element wire of each strand of the single-layer annular strand cable.
The wire cable for window regulators of automobiles is a representative example of wire cables, consisting of a plurality of strands each having one steel core element wire. The conventional wire cable for window regulators of automobiles has the following structure.
FIGS. 1a and 1b are sectional views of conventional wire cables for window regulators of automobiles. As shown in the drawings, the representative examples of conventional wire cables for window regulators of automobiles typically have two element wire structures: an 8xc3x977+1xc3x9719 element wire structure and a 7xc3x977 element wire structure. In the element wire structure of the wire cable 11 of FIG. 1a, the numeral xe2x80x9c8xe2x80x9d denotes the number of external strands 11B, xe2x80x9c7xe2x80x9d denotes the number of element wires in each external strand 11B, xe2x80x9c1xe2x80x9d denotes the number of core strand 11A, and xe2x80x9c19xe2x80x9d denotes the number of element wires of the core strand 11A. In the wire cable of FIG. 1b, the numeral xe2x80x9c7xe2x80x9d positioned at the front denotes the number of strands, while the numeral xe2x80x9c7xe2x80x9d positioned at the back denotes the number of element wires in each strand.
That is, in order to produce the double-layer twisted core strand 11A of the wire cable 11 having the 8xc3x977+1xc3x9719 element wire structure, six internal element wires are primarily twisted around one core element wire to form an internal layer around the core element wire. Thereafter, twelve external element wires are secondarily twisted around the internal layer to form the double-layer twisted strand structure of the core strand 11A. On the other hand, each single-layer twisted external strand 11B of the wire cable 11 is produced by twisting eight internal element wires around one core element wire to form the single-layer twisted strand structure of the external strand 11B. Eight external strands 11B are, thereafter, twisted around the core strand 11A to form a desired wire cable 11 having the 8xc3x977+1xc3x9719 element wire structure. In order to produce the wire cable 12 having the 7xc3x977 element wire structure, six internal element wires are twisted around one core element wire to form a single-layer twisted strand. After a plurality of single-layer twisted strands, six strands used as external strands 12B are twisted around one strand used as a core strand 12A, thus forming a desired wire cable 12 having the 7xc3x977 element wire structure.
Of the two types of wires cables 11 and 12, the wire cable 11 of FIG. 1a has been typically used for controlling the operation of window regulators of small-sized automobiles. The wire cable 12 of FIG. 1b has been typically used for controlling the operation of window regulators of large-sized automobiles.
Since the wire cable 12, having the 7xc3x977 element wire structure, is made by twisting six single-layer twisted strands 12B as external strands around one single-layer twisted strand 12A, it has a high abrasion resistance. The wire cable 12 is thus preferably used for controlling a machine, in which the cable 12 is operated while being brought into severe frictional contact with other parts. In addition, the wire cable 12 has a simple strand structure, and so it is not likely to be broken or deformed in its structure.
When such a conventional wire cable 12 is used for transmitting power in a window regulator of an automobile while being wrapped around and passing over power transmitting rotors, such as sheaves, drums or pulleys, the wire cable 12 may be easily, undesirably removed from the rotors during an operation due to low flexibility of the wire cable. The wire cable 12 also has a low fatigue resistance due to its low flexibility, and so the cable 12 may be easily cut or broken during an operation.
The wire cable 11, having the 8xc3x977+1xc3x9719 element wire structure and designed to have improved fatigue resistance, has a double-layer twisted core strand 11A with a 1+6+12 element wire structure, in place of the single-layer twisted core strand 12A with a 1+6 element wire structure of the wire cable 12 having the 7xc3x977 element wire structure. In the wire cable 11, the element wires of the core strand 11A each have a diameter smaller than that of each element wire of the external strands 11B. The wire cable 11 having the 8xc3x977+1xc3x9719 element wire structure thus has a high flexibility and a high fatigue resistance, different from the wire cable 12 having the 7xc3x977 element wire structure.
However, the conventional wire cable 11 having the 8xc3x977+1xc3x9719 element wire structure undesirably has an excessive number of element wires of the core strand, in addition to a complex double-layer twisted strand structure complicating the process of producing the wire cables. Another problem experienced in the wire cable 11 resides in that its core element wires may be more easily cut or broken during a strand twisting process, in comparison with the wire cable 12 having the 7xc3x977 element wire structure. Such wire cables 11 are thus increased in proportion of defectives produced during a wire cable manufacturing process, and so productivity of the wire cables 11 is reduced, with a concurrent increase in the production cost of the cables 11.
It is necessary for the wire cable for window regulators of automobiles, which necessarily perform a continuous, dynamic bending action during an operation, to have a high flexibility and be free from breakage or cutting of their core element wires during a strand twisting process. It is also necessary to allow the element wires of the core strand of the wire cable to come into surface contact with each other in place of point contact, thus making the element wires of the core strand to effectively distribute the external load applied from the external strands to the core strand during an operation and preventing unexpected breakage or cutting of the element wires of the core strand, and preventing any deformation of the element wire structure of the core strand during the operation of the window regulator.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a wire cable for window regulators of automobiles, which uses a highly flexible, highly elastic and high-strength filament as the core element wire of its core strand, with the core and external element wires of the core strand being twisted to come into surface contact with each other in place of point contact, thus effectively distributing external load applied from the external strands to the core strand during an operation.
In order to accomplish the above object, the present invention provides a wire cable for window regulators of automobiles, comprising a core strand and a plurality of external strands twisted around the core strand, wherein the core strand consists of a highly flexible, high-strength synthetic resin filament used as a core element wire, and six internal element wires primarily twisted around the core element wire to form an internal layer around the core element wire, and twelve external element wires secondarily twisted around the internal layer to form a double-layer twisted strand structure of the core strand, the core strand being appropriately compressed to deform the cross-section of its element wires and bring the element wires into surface contact with each other.
That is, the wire cable of this invention includes a core strand having a double-layer twisted strand structure with an F+6+12 element wire structure. This core strand consists of a high-strength synthetic resin filament used as a core element wire (F), six internal element wires primarily twisted around the core element wire to form an internal layer around the core element wire, and twelve external element wires secondarily twisted around the internal layer to form an external layer around the internal layer. The wire cable also includes eight external strands, which have a single-layer twisted strand structure with a 1+6 element wire structure and are twisted around the core strand to form an 8xc3x977+(F+6+12) element wire structure of the wire cable in cooperation with the core strand.
In the wire cable of this invention, the element wires of the core strand, except for the core element wire, have the same diameter as that of the element wires of the external strands. The core element wire of the core strand has a circular cross-section with a diameter larger than that of each of the internal and external element wires of the core strand by 1.1xcx9c2.0 times.
The core element wire of the core strand preferably has a diameter of 0.10xcx9c0.20 mm, and has a tensile strength similar to that of the steel element wires of the core and external strands. This core element wire of the core strand is selected from high-strength synthetic resin filaments having flexibility and elasticity higher than those of the steel element wires of the core and external strands.
In the present invention, the high-strength synthetic resin filament used as the core element wire of the core strand may be preferably made of high-strength thermoplastic resin, such as polypropylene, polyethylene, polyurethane, or nylon.
In the wire cable of this invention, the highly flexible, highly elastic and high-strength synthetic resin filament, used as the core element wire of the core strand and having a tensile strength of about 50xcx9c70 kgf/mm2 similar to that of the steel element wires of the core and external strands, acts as a cushioning material capable of absorbing compression load applied from the external strands to the internal and external steel element wires of the core strand during an operation of the wire cable. The synthetic resin filament used as the core element wire thus protects the steel element wires from damage or deformation due to the compression load, and allows the steel element wires to effectively endure a repeated bending action during an operation of the wire cable.
Particularly, when a machine controlling wire cable, such as a wire cable for window regulators of automobiles, passes over sheaves or pulleys while being tensioned, the wire cable is inevitably deformed in its cross-section from a circular cross-section to an oval cross-section, in addition to having a difference in load applied to the element wires of the strands. Therefore, the conventional wire cable is inevitably deformed in its cross-section when it is used for a lengthy period of time. However, the wire cable of this invention is less likely to be deformed in its cross-section, different from the conventional wire cables, since the wire cable of this invention uses a highly flexible, highly elastic and high-strength synthetic resin filament as the core element wire of its core strand. Therefore, the wire cable of this invention is lengthened in its expected life span, and has high resistance to fatigue.
Prior to twisting the external strands around the core strand in the process of producing the wire cable of this invention, the core strand is compressed at a compression ratio of 2xcx9c10%, thus compacting the core strand.
When the core strand of this wire cable is compressed as described above, the cross-section of the internal and external steel element wires of the core strand are deformed from their original circular cross-section while coming into surface contact with each other.
Due to the surface contact of the internal and external element wires of the core strand, the entire contact area between the element wires is increased to uniformly distribute external load applied from the external strands to the core strand, thus preventing an undesired concentration of load to a part of the element wires. This finally almost completely prevents a deformation or breakage of the element wires, in addition to a deformation in the structure of the core strand.
As described above, the range of the compression ratio for the core strand is set to 2xcx9c10% for the following reasons. That is, when the compression ratio for the core strand is lower than 2%, it is almost impossible to sufficiently enlarge the contact area between the element wires of the core strand or accomplish the desired load and frictional force distributing effect of the core strand. When the compression ratio for the core strand exceeds 10%, the contact area between the element wires of the core strand is excessively enlarged to restrict a relative movement of the element wires of the core strand, thus undesirably reducing the flexibility of the core strand.
In the prior art, some wire cables for window regulators of automobiles, compressed at a predetermined compression ratio to improve the fatigue resistance of the wire cables, have been proposed. However, such a conventional wire cable is produced by compressing the cable at the external strands after completely twisting the external strands around the core strand during a cable producing process. Such a compression process undesirably damages the anticorrosion film coated on the external element wires of the external strands, thus reducing the corrosion resistance of the wire cables.
However, in the wire cable of this invention, the core strand is compressed prior to the step of twisting the external strands around the core strand, and so the anticorrosion film coated on the external element wires of the external strands is prevented from any damage, different from the conventional wire cables.